1. Field of the Invention
The present invention relates to a secondary battery, and more particularly, to a case of a secondary battery which has an improved structure at a portion where sealing portions are folded in the case for enveloping an assembled battery unit.
2. Description of the Related Art
In general, secondary batteries capable of charging and discharging are applied to the fields of advanced, apparatus such as cellular phones, notebook-type computers, computer camcorders and the like. In particular, research into the lithium secondary batteries is being vigorously conducted since they have a service life 3 times longer than nickel-cadmium (Nixe2x80x94Cd) batteries or nickel metal hydride (Nixe2x80x94MH) batteries which are in widespread use as the power source of electronic equipment and have excellent characteristics with respect to the energy density per unit weight.
Such lithium secondary batteries are classified into liquid electrolyte batteries and polymer electrolyte batteries according to the type of electrolyte used. Generally, batteries using liquid electrolyte are called lithium ion batteries and batteries using polymer electrolyte are called a lithium polymer batteries.
Lithium secondary batteries are fabricated in various shapes. Typically, cylindrical or prismatic batteries are fabricated to be mainly used as lithium-ion batteries. Lithium polymer secondary batteries have flexibility so that they are relatively free in view of shape design. In recent years, lithium polymer secondary batteries having excellent safety and freedom in shape design and being light-weight have been advantageously used in view of attainment of miniaturized and light-weight portable electronic apparatuses.
As shown in FIG. 1, a conventional lithium polymer secondary battery 10 includes an assembled battery unit 11 having a plurality of assembled batteries each having a positive electrode plate, a negative electrode plate and a separator interposed therebetween laminated therein, a plurality of positive electrode tabs 12 drawn out from one side periphery of the positive electrode plate and a plurality of negative electrode tabs 13 drawn out from one side periphery of the negative electrode plate, the plurality of positive and negative electrode tabs 12 and 13 forming positive and negative electrode tab groups, respectively, and positive and negative electrode terminals 14 and 15 electrically connected to the positive and negative electrode tab groups, respectively.
Also, the conventional lithium polymer secondary battery 10 includes a case 17 having a space 16 in which the assembled battery unit 11 is accommodated. The case 17 includes upper and lower case bodies which are integrally formed along one peripheral side with the other peripheral series capable of being separated.
A sealing portion 17a is provided in each of the upper and lower case bodies along the periphery of the space 16 for hermetically sealing the inside of the battery 10 when the upper and lower case bodies are welded to each other.
Here, in order to minimize the volume in packaging the battery 10, the sealing portion 17a is folded toward the sidewall of the case 17 after mounting the assembled battery unit 10 in the space 16 and then sealing the same. Then, the, sealing portion 17a is fixed to the sidewall of the case 17 when folded, using separately provided adhering means.
According to the conventional lithium secondary battery 10, an embossing treatment is employed for improving airtightness. However, the embossing treatment makes it difficult to fold the sealing portion 17a while improving airtightness. Also, it is not easy to install a protection circuit module which is separately provided for the battery 10. Further, since the positive and negative electrode terminals 14 and 15 partially protrude outside the case 17, they are susceptible to deformation at protruding parts from one side of the case 17.
To solve the above problems, it is an object of the present invention to provide a case of a secondary battery having an improved structure in which the sealing portion in the periphery of a case can be easily folded.
It is another object of the present invention to provide a case of a secondary battery having an improved structure in which the deformation of positive and negative electrode terminals can be prevented.
Accordingly, to achieve the above object, there is provided a case of a secondary battery, the case having a space in which an assembled battery unit consisting of a positive electrode plate, a separator and a negative electrode plate, is accommodated, and sealing portions welded along the periphery of the space, wherein at least one notch portion is formed in the sealing portions.
Also, the notch portion preferably has a predetermined curvature so as to be closely fixed and folded toward the side wall of the case.
Further, the notch portion is preferably formed along the periphery of the space.
Also, the notch portion may include a first notch formed in the vicinity of the space along the periphery thereof, and a second notch spaced a predetermined distance apart from the first notch for preventing the sealing portions from partly protruding outside the case due to the longer width of the sealing portion than the depth of the case.
Here, the portion where the notch portion is formed is preferably sealed by a surface-contact method and the sealing portions excluding the notch portion are preferably embossed to maintain airtightness.